1. Field of the Invention
The present invention relates generally to the field of high power light emitting diodes, and more particularly to white gallium nitride diodes.
2. Description of the Prior Art
Gallium nitride (GaN) based light emitting diodes (LEDs) are an important source of solid state lighting in the UV through green portion of the spectrum. A white spectrum LED cannot be generated directly from GaN material, nor any other know semiconductor. The current method, therefore, for generating solid state white light consists of fabricating a blue or UV GaN LED chip and applying a variety of phosphors (e.g. Yitrium Aluminum Garnet—YAG) on top of the chip during packaging. The phosphor absorbs the blue or UV chip radiation, and re-radiates a white spectrum radiation.
The composition, thickness and uniformity of the phosphor layer are critical in determining the quality of the resulting white light, including such parameters as brightness, Color Rendering Index (CRI) and color temperature. This conventional approach of applying the phosphor during packaging significantly complicates the packaging process, and limits the use of solid state white light sources. Furthermore, over time the phosphor layer often interacts with the GaN chip, the wire bonds, or the epoxy used to encapsulate the LED package, resulting in degradation over time and reduced lifetimes.